Walls and ceilings made from gypsum wallboard are conventionally constructed by attaching the wallboard panels to framing members or studs, and filling and coating the joints between the panels with a specially formulated composition called a joint compound. Joint compounds may be powdered compositions designed to be mixed with water at the jobsite or may be premixed with water at the factory to yield a ready mixed (or paste) joint compound. Joint compounds are known in the art, and exemplary compounds are disclosed in commonly assigned U.S. Pat. Nos. 4,454,267; 4,686,253; 5,746,822; 6,228,163; 6,406,537; 6,476,009; 6,545,066 and 6,673,144 all of which are incorporated by reference. A paste joint compound (Taping grade) is placed within and over the joint formed by the abutting edges of the wallboard panels, and a paper reinforcing tape is embedded in the joint with the joint compound which is then permitted to dry. Alternately, the reinforcing tape may be of non-cellulose composition, but of a size and shape similar to strips of paper joint tape. Alternately, the reinforcing tape may be of a fiberglass weave requiring the use of chemically setting type joint compounds. When the joint compound is dry, a second joint compound (Topping or Finishing grade) is applied over the joint, and it too is permitted to dry. It is usually necessary for a third application of a joint compound and, after that third coat is dry, it may be lightly sanded and may be conventionally finished with a decorative material (paint, texture or wallpaper) then applied to the wall. All three coats of joint compound may alternately be done with an All Purpose grade of joint compound.
Ready mixed joint compound is typically supplied to the customer in either cardboard cartons having a plastic liner or plastic pails in units having volumes of 3.5 to 4.5 gallons (13.25-17.03 L). When packaging ready mixed joint compound in pails, often plastic film or coated paper liners are placed over the surface of the joint compound prior to the lid being placed and secured to reduce or delay dry out of the ready mix in the package.
Joint compound is supplied at a viscosity typically higher than what is applied at the jobsite. The higher shipping viscosity is often preferred by the joint compound manufacturer to achieve greater stability of the product in the packaging as it ages on the shelf before it is used at the jobsite. The contractor must find and mix in additional water at the jobsite using a powerful drill and mixing paddle to achieve the desired lower application viscosity. Compound that is too thin, or thinned to typical jobsite use viscosities when produced at the factory, can have problems with settling and syneresis (liquid separation). Typical shipping viscosities for joint compounds range from 400 to 800 Brabender Units (BU), while jobsite viscosities typically range from 180 to 380 BU.
Thinning of the joint compound at the jobsite usually involves addition of water through measuring methods that are inaccurate or variable. Examples of such water addition methods include two shakes of a water soaked bucket cleaning brush, various sized soft drink or coffee cups, or scoops of water from buckets using the corner of a mud pan. Even with care, these methods result in differing amounts of water added into the ready mixed joint compound and differing viscosities of the thinned compound. Obtaining water at a jobsite is often a difficulty, as on some jobsites the water supply has not yet been connected, or has been compromised by contamination from dirt and particles.
The head space between the top surface of the packaged compound and the top of the container often does not allow enough room for the addition of sufficient water needed to reduce the viscosity of the ready mixed joint compound to the desired consistency. Since the contractor usually desires to use the joint compound at a lower viscosity than that provided in the package, a conventional practice is to remove a portion of the joint compound from the package prior to the addition of water to the package, for subsequent mixing to the desired viscosity, depending on the application.
One disadvantage of this practice is that the joint compound removed must be temporarily stored for later use, or is discarded. Thus, either the contractor must have extra empty containers available for storing the unused compound, or the compound is wasted. Another disadvantage of this practice is that, as described above, the viscosity of the resulting joint compound will vary based on the amount of water added or the amount of joint compound removed, potentially resulting in inconsistent performance results.
Providing the joint compound at a ready-to-use lower viscosity, or relatively diluted state is considered undesirable due to the greater chances for phase separation over the shipping and storage period. When such relatively diluted materials generate phase separation or sedimentation, even aggressive mixing is often inadequate to restore desired uniform distribution of joint compound constituents for proper function.
The higher than desired viscosity affects the ease of pumping and moving the material out of the mixing system and through the packaging line. Thus, there are mechanical limitations on the types of raw materials that can be used within a typical wet mixing system for manufacturing ready mix.